全文获取类型
收费全文 | 283497篇 |
免费 | 6263篇 |
国内免费 | 1059篇 |
专业分类
电工技术 | 4532篇 |
综合类 | 226篇 |
化学工业 | 42589篇 |
金属工艺 | 8790篇 |
机械仪表 | 7867篇 |
建筑科学 | 7852篇 |
矿业工程 | 598篇 |
能源动力 | 7910篇 |
轻工业 | 32746篇 |
水利工程 | 2412篇 |
石油天然气 | 1988篇 |
武器工业 | 9篇 |
无线电 | 35334篇 |
一般工业技术 | 52059篇 |
冶金工业 | 54311篇 |
原子能技术 | 3543篇 |
自动化技术 | 28053篇 |
出版年
2021年 | 2513篇 |
2020年 | 1969篇 |
2019年 | 2239篇 |
2018年 | 3840篇 |
2017年 | 3850篇 |
2016年 | 4191篇 |
2015年 | 3106篇 |
2014年 | 4816篇 |
2013年 | 14272篇 |
2012年 | 8736篇 |
2011年 | 11480篇 |
2010年 | 8890篇 |
2009年 | 9702篇 |
2008年 | 10443篇 |
2007年 | 10245篇 |
2006年 | 9267篇 |
2005年 | 8290篇 |
2004年 | 7984篇 |
2003年 | 7778篇 |
2002年 | 7202篇 |
2001年 | 7368篇 |
2000年 | 6684篇 |
1999年 | 7281篇 |
1998年 | 18743篇 |
1997年 | 12812篇 |
1996年 | 9560篇 |
1995年 | 7139篇 |
1994年 | 6198篇 |
1993年 | 6048篇 |
1992年 | 4176篇 |
1991年 | 3954篇 |
1990年 | 3722篇 |
1989年 | 3520篇 |
1988年 | 3393篇 |
1987年 | 2693篇 |
1986年 | 2610篇 |
1985年 | 3308篇 |
1984年 | 2928篇 |
1983年 | 2648篇 |
1982年 | 2465篇 |
1981年 | 2520篇 |
1980年 | 2318篇 |
1979年 | 2129篇 |
1978年 | 1961篇 |
1977年 | 2323篇 |
1976年 | 3057篇 |
1975年 | 1646篇 |
1974年 | 1530篇 |
1973年 | 1609篇 |
1972年 | 1172篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Andrés Aguirre Matías Cabruja Rodolfo Cabrera Florencia Eberhardt Salvador Peirú Hugo G. Menzella Rodolfo M. Rasia 《Journal of the American Oil Chemists' Society》2015,92(1):47-53
Steryl glucosides (SG) are common contaminants in biodiesel that form precipitates, which form and cause problems due to fouling during transport and storage. Therefore, their quantification is necessary to assess the quality of this fuel. The methods currently available for SG analysis require expensive instrumentation, need a previous concentration step by solid‐phase extraction (SPE) or are of limited use for the quantitative assessment. We developed an enzymatic method for SG quantification in biodiesel samples based on the hydrolysis of the glucoside catalyzed by a broadly specific beta glucosidase and the subsequent determination of the glucose released by the reaction. The method is non‐expensive, sensitive and was adapted to 96‐well format fluorescence plate reader, making it useful for the parallel assay of multiple samples. The enzymatic assay presented here represent a valuable tool for both quality control and the development of improved biodiesel production and purification procedures. 相似文献
102.
103.
104.
Valence M. K. Ndesendo Yahya E. Choonara Leith C. R. Meyer Pradeep Kumar Lomas K. Tomar Charu Tyagi 《Drug development and industrial pharmacy》2015,41(8):1274-1287
Context and objective: The aim of this study was to develop, characterize and evaluate a mucoadhesive caplet resulting from a polymeric blend (polymeric caplet) for intravaginal anti-HIV-1 delivery.Materials and methods: Poly(lactic-co-glycolic) acid, ethylcellulose, poly(vinylalcohol), polyacrylic acid and modified polyamide 6, 10 polymers were blended and compressed to a caplet-shaped device, with and without two model drugs 3′-azido-3′-deoxythymidine (AZT) and polystyrene sulfonate (PSS). Thermal analysis, infrared spectroscopy and microscopic analysis were carried out on the caplets employing temperature-modulated DSC (TMDSC), Fourier transform infra-red (FTIR) spectrometer and scanning electron microscope, respectively. In vitro and in vivo drug release analyses as well as the histopathological toxicity studies were carried out on the drug-loaded caplets. Furthermore, molecular mechanics (MM) simulations were carried out on the drug-loaded caplets to corroborate the experimental findings.Results and discussion: There was a big deviation between the Tg of the polymeric caplet from the Tg's of the constituent polymers indicating a strong interaction between constituent polymers. FTIR spectroscopy confirmed the presence of specific ionic and non-ionic interactions within the caplet. A controlled near zero-order drug release was obtained for AZT (20 d) and PSS (28 d). In vivo results, i.e. the drug concentration in plasma ranged between 0.012–0.332?mg/mL and 0.009–0.256?mg/mL for AZT and PSS over 1–28 d.Conclusion: The obtained results, which were corroborated by MM simulations, attested that the developed system has the potential for effective delivery of anti-HIV-agents. 相似文献
105.
D. Solís-Cortés E. Navarrete-Astorga J.L. Costa-Krämer J. Salguero-Fernandez R. Schrebler D. Leinen E.A. Dalchiele J.R. Ramos-Barrado F. Martín 《Ceramics International》2019,45(5):5577-5587
C-axis textured thin films of gallium-doped indium zinc oxide (GIZO) with a 2% ratio of Ga/Zn, were obtained via RF-magnetron sputtering with high transparency and electrical conductivity. A Box-Behnken response surface design was used to evaluate the effects of the deposition parameters (In2O3 target power, deposition time, and substrate temperature) on the chemical composition, optical, electrical, and structural properties of the GIZO films. The optical constants and the electrical properties were obtained using optical models. The GIZO stoichiometry, and therefore the In/Zn atomic ratio, affected the crystallinity, crystalline parameters, band gap, and charge carrier mobility of the GIZO films. The charge carrier density was related to the change in the crystalline parameters of the hexagonal structure and the In/Zn atomic ratio. The best electrical conductivity values (1.75?×?103 Ω?1 cm?1) were obtained for GIZO films with In/Zn ratio ≥?1. Several figures of merit (FOM) defined for the visible and solar regions were comparatively used to select the optimal In/Zn atomic ratio that provided the best balance between the conductivity and the transparency. The optimal In/Zn ratio was in a range of 0.85–0.90 for the GIZO films. 相似文献
106.
107.
Chitosan microspheres containing bromocresol green, cresol red, and phenolphthalein for corrosion detection, through pH change, are synthesized in order to be used in protective coatings for aluminium alloys. Microspheres containing corrosion detection species are characterized morphologically (SEM) and physico‐chemically (FTIR, TGA). Release studies (UV–vis) are performed in corrosion‐promoting conditions (pH, NaCl), and detection studies by immersion in media associated with corrosion activity while microspheres' sensing activity is evaluated visually. Electrochemical characterization of AA2024 substrates in the presence of chitosan spheres is performed to understand material performance, and a color change is observed as a result of local pH increase in cathodic areas when corrosion takes place. These findings can be correlated with the results from release studies and seem a promising approach for corrosion sensing purposes, not only because pH increase is possible to detect due to corrosion, but also because chitosan is considered an environmentally friendly material. 相似文献
108.
Cecilia Arriagada Viviana A. Cavieres Charlotte Luchsinger Alexis E. Gonzlez Vanessa C. Muoz Jorge Cancino Patricia V. Burgos Gonzalo A. Mardones 《International journal of molecular sciences》2020,21(22)
Protein trafficking is altered when normal cells acquire a tumor phenotype. A key subcellular compartment in regulating protein trafficking is the Golgi apparatus, but its role in carcinogenesis is still not well defined. Golgi phosphoprotein 3 (GOLPH3), a peripheral membrane protein mostly localized at the trans-Golgi network, is overexpressed in several tumor types including glioblastoma multiforme (GBM), the most lethal primary brain tumor. Moreover, GOLPH3 is currently considered an oncoprotein, however its precise function in GBM is not fully understood. Here, we analyzed in T98G cells of GBM, which express high levels of epidermal growth factor receptor (EGFR), the effect of stable RNAi-mediated knockdown of GOLPH3. We found that silencing GOLPH3 caused a significant reduction in the proliferation of T98G cells and an unexpected increase in total EGFR levels, even at the cell surface, which was however less prone to ligand-induced autophosphorylation. Furthermore, silencing GOLPH3 decreased EGFR sialylation and fucosylation, which correlated with delayed ligand-induced EGFR downregulation and its accumulation at endo-lysosomal compartments. Finally, we found that EGF failed at promoting EGFR ubiquitylation when the levels of GOLPH3 were reduced. Altogether, our results show that GOLPH3 in T98G cells regulates the endocytic trafficking and activation of EGFR likely by affecting its extent of glycosylation and ubiquitylation. 相似文献
109.
C. G. Prosgolitis S. G. Lambrakos A. D. Zervaki 《Journal of Materials Engineering and Performance》2018,27(10):5102-5113
This work presents simulation of microstructure evolution in the nugget zone (NZ) of a AZ31-Mg-alloy friction stir weld. The process parameters (tool geometrical characteristics, rotational speed, travel speed, applied load) have been correlated with the resulting microstructural features in the NZ of the weld (grain size and population) with the aid of the MICRESS software, which provides the ability to simulate both nucleation and grain growth during dynamic recrystallization phenomena evolving in the NZ during the weld thermal cycle. The input parameters of the developed model include the tool geometry, the welding conditions as well as the recrystallization energy, the grain boundary mobility and specific material properties. NZ microstructure obtained by simulation shows good agreement with experimental measurements for both grain population and size. 相似文献
110.
László Lőrincz Máté Zsemberi György Bánsághi Tamás Sohajda Edit Székely 《化学工程与技术》2018,41(7):1466-1472
Chiral molecules, especially enantiomers and diastereomers of purity > 99 %, present a significant market share within the chemical, pharmaceutical, and flavor industries. Antisolvent precipitations, both batch and semicontinuous operations to serve the current trends in flow chemistry were demonstrated to be environmentally benign and efficient tools in achieving high optical purities. Although salts are known to be insoluble in supercritical CO2, instabilities of the nascent salts were detected and applied for increasing efficiency. Diastereomeric excess values of the crystalline products exceeded 99 % in maximum of three consecutive steps both by repeated resolution with half molar equivalent of the amine to the acid and by direct recrystallization of the salts. 相似文献